I looked at some pictures of Maroondah Dam and it didn't look like it would work for bungee jumping. I think I said so when I posted the sighting there. The dam is much wider at the bottom than the top, so you'd have to have a platform that stuck out 50 or 100 feet from the top of the dam to avoid hitting the face of the dam on your way down. On top of that, it's not a particularly tall dam, maybe 150 feet or less, so it wouldn't be a long drop or dramatic visually. I don't know what they did at the dam, but I'd be surprised if it was bungee jumping.
And the different versions also tend to use existing bungy sites for safety reasons. Last time I checked, there's no bungy jumping sites in Victoria that are anywhere near high enough for a TAR to use - if memory serves, the highest is less than 100 feet.
If the task at the dam is as terrifying as stated, I'd put money on it being skydiving - Lilydale Airport is less than ten minutes flight time away, and the dam's has plenty of spare room for landing. We've already got abseiling in the Blue Mountains, so it can't be that, and there's not enough native wildlife in the area for an animal task, but Healesville Sanctuary (probably the best place in the country to do touristy crap like looking at koalas and kangaroos) is in the same area as well.